fix(aya): XdpFlags default value use XdpFlags::SKB_MODE

XdpFlags type is u32, use `#derive(Default)` u32 default value is 0,
XdpFlags does not define a value of 0.

to implement Default value use XdpFlags::SKB_MODE.

Signed-off-by: Xiaobo Liu <cppcoffee@gmail.com>

aya/src/programs/xdp.rs

@@ -42,7 +42,7 @@ pub enum XdpError {
 
 bitflags::bitflags! {
     /// Flags passed to [`Xdp::attach()`].
-    #[derive(Clone, Copy, Debug, Default)]
+    #[derive(Clone, Copy, Debug)]
     pub struct XdpFlags: u32 {
         /// Skb mode.
         const SKB_MODE = XDP_FLAGS_SKB_MODE;
@@ -57,6 +57,12 @@ bitflags::bitflags! {
     }
 }
 
+impl Default for XdpFlags {
+    fn default() -> Self {
+        Self::SKB_MODE
+    }
+}
+
 /// An XDP program.
 ///
 /// eXpress Data Path (XDP) programs can be attached to the very early stages of network